<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        .per{
            width: 300px;
            height: auto;
            border:2px solid #aaa;
        }
        .li{
            width: 100px;
            height: 100px;
            background: red;
            margin: 5px;
            float: right;
        }
    </style>
</head>
<body>
<div class="per">
    <div class="li"></div>
    <div class="li"></div>
    <div class="empty"></div>
</div>
</body>
</html>
